Pentamethylquercetin (PMQ) reduces thrombus formation by inhibiting platelet function
received: 14 January 2015 accepted: 12 May 2015 Published: 10 June 2015
Ming-Lu Liang1,2, Xing-Wen Da1,2, Ao-Di He1,2, Guang-Qiang Yao1,2, Wen Xie1,2, Gang Liu1,2, Ji-Zhou Xiang1,2,3 & Zhang-Yin Ming1,2,3 Flavonoids exert both anti-oxidant and anti-platelet activities in vitro and in vivo. Pentamethylquercetin (PMQ), a polymethoxylated flavone derivative, has been screened for anti-carcinogenic and cardioprotective effects. However, it is unclear whether PMQ has anti-thrombotic effects. In the present study, PMQ (20 mg/kg) significantly inhibited thrombus formation in the collagen- epinephrine- induced acute pulmonary thrombosis mouse model and the ferric chloride-induced carotid injury model. To explore the mechanism, we evaluated the effects of PMQ on platelet function. We found that PMQ inhibited platelet aggregation and granule secretion induced by low dose agonists, including ADP, collagen, thrombin and U46619. Biochemical analysis revealed that PMQ inhibited collagen-, thrombinand U46619-induced activation of Syk, PLCγ2, Akt, GSK3β and Erk1/2. Therefore, we provide the first report to show that PMQ possesses anti-thrombotic activity in vivo and inhibited platelet function in vitro, suggesting that PMQ may represent a potential therapeutic candidate for the prevention or treatment of thrombotic disorders.
Thrombotic diseases, such as acute myocardial infarction, acute pulmonary embolism and ischemic stroke, have become the main cause of death in the modern world. It is well established that platelets play a central role in thrombotic diseases1. Platelets rapidly adhere to the subendothelial matrix as a result of endothelial cell injury and aggregate with each other to form hemostatic thrombi that prevent blood loss and maintain vascular integrity. This function must be tightly regulated because dysregulated thrombus formation causes blockage of blood vessels, which leads to ischemia2. Flavonoids are polyphenolic compounds naturally present in plants. They were discovered in the 1930s and initially considered to be vitamins because of their effects on capillary permeability. However, epidemiological studies in the 1990s showed that a greater intake of flavonoids was associated with a reduced incidence of cancer and cardiovascular disease3. Two mechanisms have been proposed to explain this protective effect, namely the inhibition of low density lipoprotein (LDL) oxidation and the inhibition of platelet aggregation4. Quercetin, a flavonoid compound, is widely distributed in plants and present in several fruits and vegetables3. Solid evidence showed that, in vitro, quercetin exerts anti-oxidant effects, a protective effect on nitric oxide and endothelial function under conditions of oxidative stress and the inhibition of platelet aggregation and LDL oxidation3. Rechner et al. demonstrated that dietary polyphenolic compounds inhibits platelet aggregation5, and Hubbard et al. reported that following ingestion of quercetin, collagen-induced platelet aggregation was inhibited6. Furthermore, previous studies have shown that the ingestion of quercetin-rich foods and beverages reduced the platelet aggregation caused by different agonists7–9.
Department of Pharmacology, School of Basic Medicine, Tongji Medical College of Huazhong University of Science and Technology, 13 Hangkong Road, Wuhan 430030, China. 2The Key Laboratory for Drug Target Research and Pharmacodynamic Evaluation of Hubei Province, Wuhan 430030, China. 3The Institute of Brain Research, Huazhong University of Science and Technology, 13 Hangkong Road, Wuhan 430030, China. Correspondence and requests for materials should be addressed to Z.-Y.M. (email: [email protected]
) Scientific Reports | 5:11142 | DOI: 10.1038/srep11142
Figure 1. Chemical structure of 3,3',4',5,7-pentamethylquercetin (PMQ).
Although quercetin exhibits a wide range of useful pharmacological properties, there are still many problems with the application of quercetin, such as, low oral bioavailability, a short elimination half-life and low titer. These shortcomings restrict its further development and utilization10. During metabolic transformation, the structural modification of quercetin had a profound effect on bioactivity11. Specifically, the full methylation of dietary flavonoids results not only in a dramatic increase in their hepatic metabolic stability but also in great improvement of their intestinal absorption, both of which should greatly increase their oral bioavailability12,13. Bernice et al. found that the metabolites of methylated quercetin have a greater ability to penetrate cells than those of quercetin10,14. According to previous studies, the bioavailability and metabolic stability of a methylated form of quercetin, 3,3',4',5,7-pentame thylquercetin (PMQ) (Fig. 1) were more desirable than those of quercetin15. PMQ is a typical member of the polymethoxylated flavones family16. Substantial evidence has emerged demonstrating the health benefits of PMQ, including anti-carcinogenic and cardioprotective properties15. However, no studies have assessed its anti-thrombotic and anti-platelet effects. Therefore, the present study aimed to investigate the effects of PMQ on thrombosis and platelet function. Moreover, we reveal the potential effects of PMQ on the collagen-, thrombin- and U46619-stimulated platelet signaling pathways.
Effect of PMQ on collagen-epinephrine-induced acute pulmonary thrombosis in mice. To investigate the effect of PMQ on thrombosis in vivo, the collagen-epinephrine-induced acute pulmonary thrombosis mouse model, in which platelet activation is induced by tail vein infusion of collagen and epinephrine, was set up as previously described17. As shown in Fig. 2A, intravenous injection of a mixture of collagen and epinephrine resulted in a mortality rate of 100% in the model mice. Treatment with 50 mg/kg aspirin had an anti-thrombotic effect, and 90% of the challenged mice survived. PMQ was also effective in preventing thromboembolic death. However, the survival rates of the animals did not differ significantly when the dose of PMQ was increased from 10 mg/kg to 20 mg/kg. Histological examination of lung tissue from model and vehicle animals revealed platelet thrombi throughout the pulmonary vasculature (Fig. 2B). In contrast, the lungs of mice injected with either 10 mg/kg PMQ, 20 mg/kg PMQ, or 50 mg/kg aspirin were largely devoid of platelet thrombi. Effect of PMQ on ferric chloride-induced arterial thrombosis in vivo. To further investigate the effects of PMQ on platelet-mediated thrombosis in vivo, blood flow through the carotid artery in C57BL/6 mice was measured following ferric chloride injury. According to the above results, we tested vehicle, 10 mg/kg PMQ, 20 mg/kg PMQ and 50 mg/kg aspirin. In model mice and vehicle-treated mice, nearly complete vessel occlusion occurred within the first 12 min following ferric chloride-induced carotid artery damage (Fig. 3A,B). As expected, aspirin 50 mg/kg (positive control) maintained blood flow at levels almost the same as pre-injury levels; similar blood flow levels were observed with 20 mg/ kg PMQ (Fig. 3D,E). When we calculated carotid blood flow after ferric chloride injury, we found that 10 mg/kg PMQ, 20 mg/kg PMQ, and 50 mg/kg aspirin significantly improved arterial blood flow during the 12 min following injury compared with the vehicle group (Fig. 3F). These results demonstrate that PMQ prevents thrombosis in vivo. PMQ inhibits human platelet aggregation induced by various agonists. As platelets have a central role in thrombosis, we investigated the consequences of PMQ treatment on platelet function and performed in vitro aggregation studies. PMQ exhibited a dose-dependent inhibitory effect on
Scientific Reports | 5:11142 | DOI: 10.1038/srep11142
Figure 2. PMQ- or aspirin-treated mice were protected from microvascular thrombosis. Mice were pre-treated with vehicle, 10 mg/kg PMQ, 20 mg/kg PMQ, or 50 mg/kg aspirin for 30 min prior to injury with intravenous injection of collagen (3.57 mg/kg) and epinephrine (0.143 mg/kg). (A) PMQ was effective in preventing collagen-epinephrine-induced thromboembolic death (n = 10). *** p